On a test bench for motor vehicles, for instance a roller test bench, or for motor vehicle components, such as an engine test bench, a transmission test bench, etc., a test object is subject to a test run and therefore developed or tested with reference to certain questions. To this end, during the test run, by means of suitable measurement sensors, certain measurement variables are detected and, generally in real time, evaluated. A test run is a temporal progression of states of the test object, such as a torque and/or speed, which are set on the test bench by means of actuators or control elements. Moreover, the test object is normally provided at the same time with certain mediums, like water, air, fuel, lubricants, etc., and information, such as control commands, measurement values of mounted sensors, simulated measurement values, etc. The test object is connected to a load machine (often called dyno or dynamometer), which loads the test object according to the test run with a load, such as a positive or negative load torque, or an speed value or a loading condition in general. The test object is operated, according to settings of the test run, against this load or this loading condition.
A test object generally is composed of a combination of a number of real components and a number of virtual components, wherein the real components are mounted as real components on the test bench and the virtual components are provided as simulation models in real time, and are therefore simulated and complement the real components. For example, on a test bench, a real internal combustion engine may be mounted, which is mechanically connected to a dynamometer. The internal combustion engine and the loading machine are controlled according to the test run, for example by adjusting a throttle valve of the internal combustion engine and by setting a setpoint torque or a setpoint speed of the loading machine, which causes a state of the test object and of the load. In order to obtain a realistic test run, or for other reasons, the components of the test object missing on the test bench, such as a gearbox, the drive train, tires, the interaction with the environment of the test object (such as the tire-road contact), etc., are simulated by suitable simulation models (“virtual components”). At the interfaces between these various real and virtual components, various physical variables, such as for example the speeds and torques, may be exchanged. According to the configuration of the test object, therefore, for the various components of the test object, various speeds and torques are required, which have to be provided for the test run.
On a test bench normally torque generators are assumed that generate a torque for driving other components or for changing their status (for instance in order to accelerate them). In a motor vehicle, the torque generator is composed of an internal combustion engine, or for example the electric starter generator. In the area of electric mobility, the torque generator is composed of an electric motor. In the case of hybrid vehicles, the torque generator may also be a combination of an internal combustion engine and an electric motor, wherein the generated torques may be positive, negative or even zero. Such a torque generator generates a torque which is called “inner torque.”
In the case of an internal combustion engine, the inner torque is generated, as a thermodynamically induced torque, by the combustion in cylinders. Due to the combustion, periodic torque oscillations are formed, which are typical of internal combustion engines. However, the inner thermodynamically induced torque of an internal combustion engine cannot be directly measured, but is instead estimated from other measurement variables, or may be determined by an indicating measuring technique. An estimation is for instance described in S. Jakubek, et al., “Schätzung des inneren Drehmoments von Verbrennungsmotoren durch parameterbasierte Kalmanfilterung”, Automatisierungstechnik, 57 (2009) 8, pages 395-402, wherein in this case the inner torque is set equal to a propulsion torque. In the indicating measuring technique, as is well-known, thermodynamic characteristic variables of an internal combustion engine (indicating variables), in particular the inner pressures in the cylinders of the internal combustion engine, are detected and resolved over the crank angle (or equivalently over time) or are averaged over a period or a working cycle or other mechanisms. Then, through the indicating variables, by means of known methods, the inner thermodynamically indicated torque of the internal combustion engine may be calculated. This happens if necessary also resolving in synchronism with the crank angle, or over a working cycle (in case of a 4-stroke engine, for example, two rotations) or by averaging or other processing through other filtering or mechanisms. These indicating variables are partially known also to the engine control unit of internal combustion engine, or are determined in the engine control unit and may then also be read from the engine control unit, and be provided in this way, optionally in real time, if possible.
In the case of an electric motor, the inner torque is the electrically indicated torque, which is active between the rotor and stator, the so-called air gap torque. This air gap torque may for example, as already known, be calculated from a measurement of current and voltage of the electric motor. The air gap torque may, however, also be measured directly by specific commercially available indicating measuring techniques. In the same way, the air gap torque may also be read, as an inner torque of the electric motor, from an electromotor control unit.
For a test run, normally and conventionally a measurable shaft torque on a shaft output of a real component is also used. This shaft torque may be detected on the test bench by means of suitable measuring sensors in a known way, or it may be estimated from the electric torque of the dynamometers and/or a known pendulum support mounted on the test bench. Beyond the torque, on the test bench normally also the rotational angle is measured.
For a test run, in particular for the stimulation of the virtual components of the test object, the propulsion torque is however frequently of interest. This is the torque which the torque generator may effectively provide for driving a load and for changing the status (acceleration, braking) of the mass inertias present.
However, besides the inner torque and the shaft torque, further torques, such as for example torques generated by certain secondary arrangements (such as a cool water pump, a conditioning compressor, an oil pump, starter engine/generator, etc.), friction torques, or losses caused by oscillations of the internal combustion engine act on the mass inertias of the real component of the test object (such as for instance the crank shaft of an internal combustion engine or an engine shaft of an electric motor). The shaft torque which can be detected on the test bench therefore normally does not correspond to the propulsion torque of the torque generator of interest. Such further torques are also not easily, if at all, detectable, so that often from the measured shaft torque a high-quality propulsion torque cannot be deduced by calculation, which may be used for simulation of virtual components of the test object.
This is also due to the fact that for many test object configurations (combination of real and virtual components), the measurement signal for the shaft torque is very noisy, for instance when on the output shaft of the torque generator a rotation damper such as a double mass flywheel is actually arranged or coupling plays are present. In the same way, the measurement signal for the shaft torque is frequently not sufficiently resolved, temporally and/or in the measurement range. Apart from this, the shaft torque is not detected by measurement in all test bench configurations, so that the shaft torque is also not always available. In this case the torque of the dynamometer or of a bending beam may be available and used, wherein such a torque can only approximate the shaft torque.
Similar problems may arise for the measurement signal of the rotation angle, the angular velocity and the angular acceleration, which also may not be sufficiently resolved in time or measurement range.
Moreover, on the test bench the problem often arises that the auxiliary devices aren't actually present, wholly or in part. Therefore, the torques detected on the bench (shaft torques, indicating torques, etc.) would also not be the propulsion torque of interest, which, for example, would be used for a simulation of the internal combustion engine as a part of a virtual vehicle in a vehicle simulation environment.
Based on the previous explanations, it can also be seen that also the measurable torques, whether thermodynamic and/or electric, the sum of which is indicated as the “inner torque,” cannot be used as a propulsion torque. Moreover, on the test bench all cylinders are not always actually present (for instance in case of a one-cylinder test engine) or not all cylinders are indicated with an indicating measuring technique in order to detect indicating variables.